Magnetic fluid or ferrofluid magnetic seals have been used as exclusion seals or as multiple-stage seal apparatuses, where a difference in pressure environments is involved. Ferrofluid exclusion seal apparatuses are particularly useful in providing effective seals in computer-disc-drive systems and in other high-performance precision spindle applications. The difficulties associated with the application of the particular ferrofluid or magnetic fluid into the seal by the user, either exclusion seals or multiple-stage seals, have led to the development of self-activating fluid seal apparatuses, such as described in U.S. Pat. Nos. 4,252,328 and 4,252,353, both issued Feb. 24, 1981 (both hereby incorporated by reference).
In U.S. Pat. No. 4,252,328, a self-activating ferrofluid seal apparatus is described which is particularly useful with a memory disc-drive shaft, wherein the seal apparatus contains a cavity between the pole pieces, and a closed loop of a tubular container with a sealing amount of ferrofluid is positioned within the cavity. Just prior to insertion of the magnetically permeable shaft element to be sealed, a penetration clamp is employed to penetrate the plastic tubular container, to permit the ferrofluid in the container to move from the container into a sealing relationship in the radial gap about the ends of the pole pieces.
In U.S. Pat. No. 4,252,353, a self-activating seal apparatus is disclosed, wherein the pole pieces form a cavity for storing a sealing amount of a ferrofluid, until the magnetically permeable shaft is inserted within the seal apparatus. The ferrofluid is retained within the cavity generally adjacent the intersection of the magnetic ring element and the first and second pole pieces, while a nonmagnetic sealing ring is also employed to retain the sealing volume of ferrofluid within the cavity in the stored position. On removal of the nonmagnetic ring element and the insertion of the magnetically permeable shaft, the magnetic field is so altered and the flux path diverted from the intersection of the permanent-magnet ring element and the pole pieces to the radial gap separating the ends of the pole pieces and the surface of the shaft element, so that the ferrofluid then forms a self-activating, ferrofluid, O-ring seal with the surface of the shaft element. While such self-activating ferrofluid seal apparatuses are effective, it is desirable to provide for a self-activating seal apparatus and method of improved design, cost and simplicity.